1. Field of the Invention
This invention relates to optical projection apparatus and, more particularly, to means for generating a light beam of substantially uniform intensity from a multi-element light source initially projecting a beam having a generally Gaussian intensity distribution.
2. Description of Related Art
A laser is a source of high intensity, coherent, monochromatic light that has a number of diverse applications. The laser beam is often generated from a nonplanar array of discrete, mutually spaced light sources such as commonly found in GaAs laser diode arrays. In most applications, it is desirable to convert the light from the nonplanar multi-element source into a substantially uniform flat or planar luminous source. U.S. Pat. No 3,535,507 to Sugino discloses one particularly advantageous method of accomplishing this objective. Briefly, this is accomplished by passing the light through an axially elongated optical duct comprising a body of optical material with totally reflecting side faces, as well as flat entrance and exit faces perpendicular to the optical axis. The body of optical material effectively integrates or homogenizes the discrete nonplanar light sources into a uniform planar beam.
While the above-mentioned patent teaches an advantageous method of generating a planar beam from a plurality of discrete nonplanar sources, the output beam still does not have a uniform distribution of light intensity across its diameter. The technical literature reports several problems that are associated with the non-uniform light intensity distribution of laser beams (see, e.g., P. W. Rhodes et al, "Refractive Optical Systems for Irradiance Redistribution of Collimated Radiation: Their Design and Analysis", Applied Optics, Vol. 19, No. 20, Oct. 15, 1980). The intensity of a laser beam generally follows a Gaussian distribution, i.e., the beam is more intense along the central optical axis. The high central irradiation is a potential eye hazard when using high powered lasers unless suitable precautions are taken. Still other problems associated with the Gaussian distribution is that it dramatically reduces the optical efficiency in optics such as telescopes with central obscuration.
In an attempt to redistribute the radiation of laser beams, the authors of the above-noted article disclose the use of aspheric refracting elements to normalize the output of the beam to a uniform energy distribution. Some of the drawbacks with this approach include the requirement for at least two additional lenses in the optical system thereby increasing cost, set up time, and other problems that are appreciated by the skilled practitioner.